1. Field of the Invention
The present invention relates to peristaltic pumps with deformable tubing.
2. Description of the Related Art
In general, peristaltic pumps are composed of a frame to which is fastened a motor whose shaft rotates a cage comprising a plurality of rollers. The rollers are in contact with a deformable tubing that they compress until it is sealed. The angular displacement of the point of sealing causes, behind the compressed zone, a vacuum in the tubing that immediately fills with fluid. The amount of fluid trapped in the deformable tubing between two rollers is then propelled to the outlet of the pump. A liquid, pumped at an open end of the deformable tubing, called the intake or upstream end, is thus conveyed to the other end of the deformable tubing, called the delivery or downstream end. Most peristaltic pumps comprise a casing having a cylindrical inner surface, called the bearing surface, against which the tubing is compressed by the rollers to seal it. The envelope swept by the paths of the outer surfaces of the rollers is called the runway or rolling path.
The main component of a peristaltic pump is its pump body tubing, which is generally made of elastomer. The pump body tubing is made by extrusion. The physical and dimensional properties of the tubing given by the manufacturer are only average values. The measured values of a particular property fluctuate statistically, for example according to Gauss' Law, about the corresponding average value. The deformable tubing manufacturer defines a tolerance interval around the average value in which there is an increased probability of finding the measured value of the property. The measured thickness of a deformable tubing at the point where it is deformed fluctuates about the average value. It is therefore probable that the portion of deformable tubing compressed by the rollers has walls whose combined thickness is less than or greater than the nominal sealing dimension provided for by the pump manufacturer. Incidentally, the sealing of the pump body tubing, characterized by the sealing dimension, consists in first placing the two walls of the tubing in contact and then applying an appropriate clamping action depending on the thickness of the tubing, its hardness, the temperature, etc.
Similarly, during the use of the deformable tubing, the wall suffers from wear, swelling, loss of thickness, modification of the physical nature of the material of which the tubing is made, etc. This wear in the broad sense may be due to the repeated mechanical action of the rollers on the outer surface of the tubing, to the chemical action of the liquids conveyed within the tubing on the inner surface of the tubing, or to the conditions under which the peristaltic pump is used, for example temperature. Consequently, the combined thickness of the walls of the deformable tubing tends to vary over time. The time comes when the cumulative thickness of the walls becomes less than or greater than the nominal sealing dimension.
When the nominal sealing dimension is not complied with, either the peristaltic pump becomes less efficient because the seal is not achieved, or the excessive thickness leads to excessive clamping, increasing the resistive torque of the peristaltic pump.
For a given type of tubing, there is therefore a need for a peristaltic pump that can compensate for variations in the properties of the tubing.
Moreover, it must be possible for a user to be able to replace a first tubing by a second pump body tubing rapidly. The adjustments required in order for the peristaltic pump to be able to operate with a second tubing must be easy to carry out, and preferably automatic, minimizing risks of error.
Moreover, in the medical field in particular, the deformable tubing must be completely changed for each new application, in particular for reasons of hygiene. There is a permanent need to simplify the consumable so as to increase the number of parts that can be reused from one application to the next, to reduce the operating cost of the pump and the number of components, often made of plastic, that are thrown away on each new application.
To solve these various problems, the manufacturers of peristaltic pumps have to find mechanical solutions that will guarantee sealing. The best known solutions consist in mechanically varying the radial distance between the inner surface of the bearing surface and the rolling paths of the rollers on the pump body tubing.
Patent SU 1 262 106 of 7 Oct. 1986 discloses an improved peristaltic pump for limiting fluctuations in flow rate during use. The flexible tubing is in this case compressed between a plurality of rollers and a flexible U-shaped strip. The curve of the flexible strip is set by tangential adjustment pins connected to the ends of the flexible strip and radial adjustment pins connected to a central portion of the flexible strip. By turning the adjustment pins to a greater or lesser extent, the user gives the flexible strip an optimum shape.
The deformable tubing is compressed until it is sealed only against the central portion of the flexible strip whose profile is an arc of a circle with an opening of 360°/κ and a radius r1=r0+2e (where κ is the number of rollers and r0 is the radius of the rolling path run by the rollers). The profile of the input and output sections is curved and follows the equation r2=r1+D 2r (where r is the internal radius of the tubing and D a parameter corresponding to the degree of compression of the tubing varying between 0 and 1).
That document does not describe how the deformable tubing is inserted between the flexible strip and the rollers. Although in the above equations the thickness and the radius of the deformable tubing are in the form of parameters, the use of deformable tubing having variable properties is not discussed. No particular information about the variation of the parameter D along the input and output sections is given in order to define the optimum profile. Lastly, the curve of the flexible strip is adjusted manually by the user during operation of the pump.
Patent SU 794 243 of 7 Jan. 1981 describes a peristaltic pump whose tubing support is wound to form a helical turn around a roller mounted on a shaft that is off-centre with respect to the axis of the helix. The deformable tubing is placed between the roller and the tubing support. The tubing support consists of a metal strip having a degree of elasticity whose tubing ends are joined by an adjustment screw. When the user turns the screw, the two ends of the strip move towards or away from one another. As a result, the radius of the helix is modified to change the distance between the tubing support and the roller to modify the occlusion of the deformable tubing making it possible to compensate for the thickness of the tubing.
Moreover, the tubing support is connected to the frame by a series of bolts that are distributed regularly in an annular arrangement, each engaged in a guide groove. The guide grooves, whose shape is not described, make it possible indirectly to limit the displacement of the tubing support so that it has a constant radius of curvature all along its length. Once the user has made the adjustment, the bolts are tightened, which prevents any modification of the radius during operation of the pump.
Lastly, U.S. Pat. No. 5,549,461, granted on 27 Aug. 1996, discloses a peristaltic pump comprising an occluder ring linked to a hinged support by means of a series of threaded bolts. While the rollers are turning, the hinged support is lowered so that the deformable tubing is compressed against the occluder ring, thus functioning as a clutch for the pump. In the lowered position, the hinged support is kept against the frame by a closure system that prevents excessive pressure if necessary. The radius of the occluder ring, which is concentric with the axis of rotation of the rollers, can be adjusted by the user by means of a series of screws to allow the pump to be used with deformable tubing of different thicknesses.
The peristaltic pump described is not made for delicate laboratory or medical applications. The curvature of the ring and the means of obtaining it by screwing the bolts are not described.